The United States and Japan will step up their defence cooperation to deal with the threat from nuclear-armed North Korea as tensions in East Asia remain high, officials from the two allies said on Thursday.

Man on run after fatal Vic stabbing

One man is dead from stab wounds and another has fled following a fight in Melbourne's west.

The two men were involved in a fight where one of them was stabbed in the torso on a busy street in Altona North just before 3pm, Detective Sergeant Nathan Favre said.

Several people were driving past and stopped to help the man. However, he died at the scene and has not yet been identified.

At the time of the incident a female was present and is assisting police with their inquiries, Det Sgt Favre said.

Police are searching for the other man and were still investigating if the two men knew each other and what weapon was used.

"We're getting assistance from people present who believe that it was a matter between two people at the time and certainly we believe that members of the public shouldn't be alarmed that their safety is in jeopardy," Det Sgt Favre said.